1. Field of the Invention
This invention relates to useful materials and mixtures thereof for use in wetting agents, detergents and/or cleaning products and, more particularly, to a new form of preparation of this known class of materials where they are present as pourable and/or free-flowing granules. More particularly, the teaching according to the invention seeks to provide products of the type in question which are distinguished by a combination of important performance parameters for the particular field of application in question which has been difficult to achieve in the hitherto conventional production of the useful materials in question on an industrial scale.
2. Discussion of Related Art
Useful materials and mixtures thereof for use in wetting agents, detergents and/or cleaning products in the form of free-flowing granules are generally obtained by drying intermediately obtained water-containing slurries of the materials in question. For decades, preparations such as these have been universally spray-dried on an industrial scale. Hot air or mixtures of air and hot combustion gases are used as the drying gas stream.
The performance requirements which pourable and free-flowing powders, granules or even more heavily compacted particulate materials such as these have to satisfy are extremely diverse and conflict with one another in many respects. For example, the useful materials or mixtures thereof are now expected to be compacted to comparatively high apparent densities, but at the same time to dissolve quickly again in the washing or cleaning process. The use of so-called fillers, which do not play a key role in the washing or cleaning process, but which can impart an increased apparent density and, to a certain extent, improved redissolvability to the dry formulations, should be limited as far as possible or, better yet, dispensed with altogether. The content of surface-active components in the solid formulations should be increased as far as possible to satisfy the concept of the optimized active-substance concentrate. However, it is known that these surfactants (both anionic and nonionic types) have a pronounced tendency to gel, particularly when dried from water-containing slurries, so that even a fine-particle material is difficult to redissolve or may even be completely insoluble. Another important factor is the well-known temperature sensitivity of many of the useful materials in question, particularly in the presence of water. Accordingly, the production of dry pourable or free-flowing useful materials and mixtures thereof for the field of application in question, for example the industrial production of laundry detergents, has developed into a high-technology industry.
Among industrial drying processes, the technology of drying with superheated steam, which has been known for about a hundred years, has recently been attracting increasing attention. The circulation of the super-heated steam used as drying gas in a closed-circuit system and the possibility of direct condensation of the vapor stream removed from the circuit create favorable conditions for the operation of such drying installations with minimal ecologically harmful emissions. However, the practical application of this technology has hitherto been confined to non-tacky, wet particulate material. For example, superheated steam is used in the drying of lignite and sewage sludge and in the drying of beet chips, biomasses and other organic products for use in animal foods, cf. for example D. Gehrmann "Entwicklungstendenzen der Trocknungstechnik in der chemischen Industrie", Chem.-Ing. Tech. 62 (1990) A 512-520, more particularly sub-chapters 2.2 and 3.1.
Applicants have worked extensively on the possibility of applying the principle of drying with superheated steam to useful materials and mixtures thereof for use in wetting agents, detergents and/or cleaning products. It has surprisingly been found that this drying process may also be used for the present and, for various reasons, much more sensitive field of application with the hitherto known, more particularly ecological and energy-related advantages of drying with superheated steam. Thus, DE-A 40 30 688 describes a process for recovering fine-particle, solid or free-flowing useful materials or mixtures thereof for wetting agents, detergents and/or cleaning products from water-containing preparations thereof using superheated steam as the drying hot gas stream. In this process, drying of the particulate material is terminated before it is endangered by heat.
Particular embodiments of and improvements in such drying processes using superheated steam as the hot gas stream and their application to useful materials and mixtures thereof for wetting agents, detergents and/or cleaning products are disclosed in a number of other earlier applications in Applicants' name, cf. in particular earlier German patent applications DE-P 42 04 035.3, DE-P 42 04 090.6, DE-P 42 06 050.8, DE-P 42 06 521.6, DE-P 42 06 495.3, DE-P 42 08 773.2 and DE-P 42 09 432.1.
The technical teaching described hereinafter relates to an important further development of this technology of producing dry pourable or free-flowing useful materials or mixtures thereof for wetting agents, detergents and/or cleaning products. The teaching according to the invention is based in this regard on the disclosures and working principles of DE-A 40 30 688 and the earlier applications cited above. Accordingly, the disclosures of that document and the earlier applications cited above are hereby specifically included in the disclosure of the present invention which is to be understood in conjunction with the further disclosures and working principles discussed hereinafter.
The teaching according to the invention is based on the surprising observation that the use of super-heated steam as drying medium in the drying of water-containing preparations of useful materials and mixtures thereof from the field of wetting agents, detergents and/or cleaning products enables hitherto unknown combinations of important performance properties to be established in the dry product. Building on this, further embodiments of the invention provide new preparations of useful materials which have proved superior to hitherto known materials. The replacement of the conventional hot gas phase based on combustible gases or air/combustible gas mixtures by superheated steam not only improves the ecology of the process as a whole and the specifically modified chemical/thermodynamic stressing of the material to be dried, the spatial structure of the dried material primarily developed in the micro range is also clearly influenced by the use of super-heated steam as the drying medium. The teaching according to the invention makes use of this and, in doing so, provides useful materials of the described type or mixtures thereof characterized by new properties and/or new compositions.